This invention is concerned with the manufacture of camshafts, for example camshafts of the type used for operating the valves of an internal combustion engine.
Conventionally, camshafts are cast in one piece, i.e. a plurality of cams and the shaft on which they are mounted, are formed as an integral casting. This method, however, requires complex casting and hardening processes and the cast camshaft has to be finished by protracted grinding operations.
It has previously been proposed that such camshafts should be manufactured by forming the cams and the shaft separately, assembling the cams on the shaft, and securing the cams to the shaft. For example, the cams may be brazed to the shaft or the shaft may be formed as a tube which is caused to expand into gripping contact with the cams by hydraulic expansion. Such methods, however, introduce complex assembling and joining operations to ensure that the cams project from the camshaft in the correct orientations and are securely mounted on the camshaft to prevent relative movement. For example, GB Patent Specification No. 2121908A discloses an assembled camshaft having cams with V-shaped projections which fit into similarly-shaped grooves in a shaft. Cams for this camshaft would, however, be difficult to manufacture and the orientation accuracy is limited by the clearance between the projections and the grooves. Assembled camshafts have hitherto not utilised chill cast cams, i.e. cams whose surfaces are chilled as they solidify to harden them, because existing attachment methods involve heating which damages the hardened surfaces or, in the case of hydraulic expansion, tend to split the cams.